Rust is used a lot. Elixir/Phoenix comes up often. You’re looking for something statically typed with string guarantees and as FP as possible to make unit testing easier.
I've been using Rust more and more for specific tasks in my Elixir saas app, the two play really well together.
Rust for sure. Builds become a problem eventually though. Elixir is much more interesting now that they added types (I think they're doing more with this still?). I quite like Gleam from a human (non-agent) perspective.